– Prof. Hiroaki Koide of Kyoto University: ‘Massive amounts of radioactive materials will be released into the environment again’ – Fukushima Reactor Core May Have Sunk Into The Ground – ‘We are now head to head with a situation that mankind has never faced before’
– Study Shows Worse Picture of Meltdown in Japan (New York Times, Nov. 30, 2011):
TOKYO — Molten nuclear fuel may have bored into the floor of at least one of the reactors at the stricken Fukushima Daiichi nuclear power plant, the complex’s operator said Wednesday, citing a new simulation of the accident that crippled the plant in March.
The simulation suggested that the meltdown may have been more severe than had previously been thought.
Soon after an earthquake and a tsunami on March 11 knocked out cooling systems at the power plant, nuclear fuel rods in three of its six reactors overheated and slumped, the operator, the Tokyo Electric Power Company, has said.
In the No. 1 reactor, the overheated fuel may have eroded the primary containment vessel’s thick concrete floor, and it may have gotten almost within a foot of a crucial steel barrier, the utility said the new simulation suggested. Beneath that steel layer is a concrete basement, which is the last barrier before the fuel would have begun to penetrate the earth.
Some nuclear experts have warned that water from a makeshift cooling system now in place at the plant may not be able to properly cool any nuclear fuel that may have seeped into the concrete. The new simulation may call into question the efforts to cool and stabilize the reactor, but the Tokyo Electric Power Company, or Tepco, says it is not worried more than eight months after the accident.
The findings are the latest in a series of increasingly grave scenarios presented by Tepco about the state of the reactors. The company initially insisted that there was no breach at any of the three most-damaged reactors; it later said that there might have been a breach, but that most of the nuclear fuel had remained within the containment vessels.
“This is still an overly optimistic simulation,” said Hiroaki Koide, an assistant professor of physics at the Kyoto University Research Reactor Institute, who has been a vocal critic of Tepco’s lack of disclosure of details of the disaster. Tepco would very much like to say that the outermost containment is not completely compromised and that the meltdown stopped before the outer steel barrier, he said, “but even by their own simulation, it’s very borderline.”
“I have always argued that the containment is broken, and that there is the danger of a wider radiation leak,” Mr. Koide said. “In reality, it’s impossible to look inside the reactor, and most measurement instruments have been knocked out. So nobody really knows how bad it is.”